This study is designed to study the localization and characterization of adrenergic receptors in the cardiovascular system using light and electron microscopic techniques. I plan to localize alpha and beta adrenergic receptors over different regions of the conduction system using tissue sections incubated in radioligands for alpha1, alpha2 and beta receptors and processed for autoradiography using a dried emulsion layer which reduces diffusion of the ligand. Grain density over the tissue will be quantitated using a Nikon Magiscan image analyzer. Catecholamine-containing nerve terminals will be localized and quantified in adjacent blocks to determine if there is a relationship between grain density and the volume of catecholamine-containing nerve terminals. It is also proposed to localize and quantify adrenergic receptors over the heart and blood vessels of different sizes and in different vascular beds, using several concentrations of the ligand and a set of autoradiographic standards. An estimate of the dissociation constant and the maximum number of binding sites in different regions of the cardiovascular system will be obtained. For electron microscopic localization of the beta receptor, it is proposed to incubate pieces of rabbit atrium in a photoaffinity label, place the tissues under a UV light, rinse them thoroughly and process the tissues for electron microscopic autoradiography using a method to localize adrenergic nerves. The distribution of the label over the nerves, blood vessels and cardiac myocytes will then be determined. It is also proposed to localize beta receptors on the membranes of cultured cardiac myocytes using an alprenolol labelled with ferritin. The label will be initially characterized using erythrocyte ghosts mounted on electron microscope grids to determine optimal conditions for binding and tissue processing. Cultured myocytes, isolated from neonatal rat hearts will then be incubated with the label and the distribution of the label will be determined.